Frost imaging employing a deformable electrode



May 13, 1969 ,L. F. BEAN ET AL 3,443,938

FROST IMAGING EMPLOYING A" DEFORMABLE ELECTRODE I Filed May 13, 1 964 INVENTORS. LLOYD F. BEAN ROBERW. GUNDLACH irromve'rs United States Patent U.S. CI. 961.1 9 Claims ABSTRACT OF THE DISCLOSURE A deformation imaging member and method is described wherein a deformable organic conductive materlal serves as an electrode in the non-charge frost technique.

This invention relates to deformation recording and in particular, to photosensitive frost recording.

Recently, a new type of deformation recording was (118- covered called frost, which has been disclosed in U.S. patent application Ser. No. 193,277, filed May 8, 1962 now U.S. Patent 3,196,011. Generally, the recording member for frost comprised a conductive layer coated first with a photoconductive layer and second with an insulating thermoplastic layer. Frost recording in one preferred manner has been by charging the thermoplastic layer with a corona discharge device, exposing to a light pattern, recharging to a uniform potential with the corona discharge device and then heating to soften the thermoplastic layer until frost deformation occurs. The first charge step produces a uniform layer of electrostatic charges on the surface of the thermoplastic at a uniform potential. The exposure step permits charge migration through the photoconductive layer in the illuminated areas lowering the potential at the thermoplastic surface in the corresponding areas of the thermoplastic layer. The second charging step brings the surface of the thermoplastic to a uniform potential producing a variation in charge density, so that the areas that have been illuminated receive a higher number of electrostatic charges than the areas that have not received illumination. Upon lowering the viscosity of the thermoplastic layer, as by heating, a fine-grain, random deformation of the thermoplastic surface occurs, first in the areas having the highest charge density.

It is sometimes desirable to avoid corona charging, since the corona discharge requires very high voltages. A partticular problem with corona charging of a deformable material is that the corona charging process increases the tendency to collect dust and other foreign material on the charged surface. Foreign material on the thermoplastic surface tends to become embedded in the thermoplastic upon heating and thereafter is very difficult to remove. One method has been found for avoiding the use of corona discharge, which has been called internal frost. In internal frost, the member is a sandwich comprising a conductive layer, a photoconductive layer, an insulating deformable layer, a conductive deformable layer, and a conductive support layer. Voltage is applied between the first conductive layer and the conductive support layer, while deformation occurs at the interface between the insualting deformable layer and the conductive deformable layer and the conductive deformable layer. A disadvantage of this arrangement is the difficulty in obtaining high contrast. In any deformation imaging arrangement, the contrast that can be achieved is dependent in part upon the different in refractive indexes of the materials on either side of the deformed surface. As is well known, a greater difference in index of refraction can be 3,443,938 Patented May 13, 1969 obtained between a solid and a gas than at the interface between two solids.

Now in accordance with the present invention, it has been discovered that an adequately conductive layer can be applied to the deformable surface of a frost member to permit contact charging between such surface and a conductive substrate, and still permit frost deformation at the free surface. This has been found possible by applying a conductive material to the surface of the thermoplastic layer that is compliant enough to deform along with the deformation of the thermoplastic. Thus, it is an object of the present invention to define a frost member having a frost-wise deformable electrode.

Further objects and features of the invention will become apparent from reading the following description in connection with the drawings wherein:

FIG. 1 is a diagrammatic illustration of a frostable member in accordance with the invention.

FIGS. 2, 3 and 4 are diagrammatic illustrations of the flow steps of the recording method in accordance with the invention.

FIG. 5 is an isometric drawing of one embodiment of the frostable member according to the invention.

Referring now to FIG. 1, it will be seen that the deformation recording member comprises a conductive layer 11, a photoconductive layer 12, a deformable thermoplastic layer 13, and a deformable electrode 15.

Layers 11, 12 and 13 make up a conventional frost member as disclosed, for example, in the aforesaid patent application 193,277. Conductive layer 11 may be a metal substrate such as aluminum, brass, or other conductive sheet material, either rigid or flexible. Conductive layer 11 may also be a transparent layer such as glasswith an evaporated coating of tin oxide, copper iodide, or the like. Photoconductive layer 12 is an insulating photoconductive material coated onto conductive layer 11 by evaporating, dip-coating, or similar process. Suitable materials are vitreous selenium, which is preferably deposited by evaporation, or organic photoconductive materials such as disclosed in Canadian Patent 611,852. The organic photoconductive materials disclosed in the Canadian patent are readily applied by dip-coating techniques. Thermoplastic layer 13 which is suitably dip-coated over the photoconductive layer 12 may be any one of a number of thermoplastic materials having high insulating qualities of 10 ohm-cm. or greater at a viscosity that is readily reduced to between 10 and 10 poises at some temperature between about and 200 F. Exemplary materials for this purpose are glycerol ester of 50% hydrogenated rosin available as Staybelite ester 5 and Staybelite ester 10 from the Hercules Powder Company, styrene and styrene homologue resins and other thermoplastic materials. A further partial listing of suitable materials may be found in the aforementioned U.S. patent application Ser. No. 193,277.

Photoconductive layer 12 may also be self-deformable to serve as both photoconductive layer and thermoplastic layer so that layer 13 is eliminated. However, a charge storage layer is desirable and in the absence of layer 13 a thin insulating layer should be provided between substrate 11 and photoconductive layer 12 to prevent conduction from layer 15 through the exposed areas of the photoconductor directly to the substrate. For this purpose, organic photoconductors in an insulating plastic are particularly suitable as photoconductive layer 12.

The thickness of the thermoplastic layer whether a selfdeformable photoconductor or not is preferably in the range of 1 to 6 microns. Thinner layers reduce maximum frost density and thicker layers show degraded resolution.

Over the thermoplastic layer, deformable electrode 15 is coated by similar techniques to those previously discussed. This deformable electrode must have a bulk conductivity of at least 2 10- mho/cm. Thin metallic layers of evaporated metal have been tried with some success, but are not considered preferred materials. If thin enough to permit ready deformation of the thermoplastic layer, the evaporated metal layers tend to break up with deleterious electrical discontinuities. This is especially true when any attempt at erasure and reuse is made. Thicker metal layer prohibit frost even though some relief deformation may be produced. Preferred materials have a viscosity fairly close to that of the thermoplastic permitting a thickness similar to that of the thermoplastic layer. If the viscosity of electrode 15 is less than that of the thermoplastic layer 13, electrode 15 willl tend to flow into the frost depressions lowering frost density. If the viscosity is greater than that of thermoplastic layer 13, it tends to restrict deformation reducing sensitivity.

One preferred material for layer 15 which has been used with Staybelite as thermoplastic layer 13, is polymerized ethylene imine in a 50% aqueous solution and having a molecular weight range of 30,000 to 40,000. The aqueous solution is diluted further in water to a viscosity of about 50 centipoises and then dip-coated at a rate to give about a 2 micron coating over the Staybelite. This coating should be at least as thin as thermoplastic layer 13. For example, a 2 micron coating may be used over a 4 micron layer of Staybelite. Coatings in the range of /z to 3 microns are suitable and about 2 microns is preferable to obtain adequate conductivity. Resolution decreases as the coating thickness is increased. The coating is then hardened by drying. Another material operative in accordance with the invention as layer 15 is Carboset XH1 avaliable from B. F. Goodrich Company.

A strip 16 of metal foil or metallized tape can be adhesively applied along one edge of deformable electrode 15 in order to provide an electrical connection.

In operation a potential is applied between strip 16 and electrode 11. An electrical charge builds up across layers 12 and 13 with charges of one polarity appearing at the interface of layers 13 and 15 and charges of the opposite polarity appearing at the interface of layers 11 and 12. The amount of charge that builds up is determined by the relationship Q=OE where Q represents the charge in coulombs, C represents the capacity of the sandwich in which layer 11 and layer 15 are the two electrodes, layers 12 and 13 are lumped as the dielectric between the electrodes, and E represents the applied potential.

While the potential is applied, the sandwich is exposed to an image pattern of light and shadow. In the areas where light strikes photoconductive layer 12, the photoconductor becomes relatively conductive and may be ignored as part of dielectric in the sandwich. This affectively reduces the dielectric thickness in the illuminated areas resulting in an increase in capacity. Referring back to the relationship Q=OE, it will be noted that C is increased in the illuminated areas while E is held constant as the applied potential. With E constant and C increasing, Q must also increase. Thus, we get a relative increase in electrical charge across layer 13 in the illuminated areas.

FIGURES 2 through 4 illustrate flow steps in image formation using the member of FIGURE 1. FIGURE 2 shows a potential source 18 applied across layers 11 and 15 while member 17 is exposed to an image by exposure system 20. After charge variations have been produced as described above, member 17 is heated for development by a heating device 21 depicted as an electric oven in FIGURE 3. Note that the photoconductor should be shielded from radiations of the heating device in the photosensitivity spectrum of the photoconductor. Heat may be applied with or without continued exposure and/ or application of potential. Heat is applied until the frost image forms by the appearance of frost in the illuminated areas. After the image has appeared member 17 is cooled to harden the image.

Erasure of the image can be obtained as illustrated in 4 FIGURE 4 by application of a relatively greater amount of heat than that used for development. Heat applied for erasure softens thermoplastic layer 13 and renders it rela tively conductive at the same time so that the charge pattern is dissipiated and surface tension removes the deformities. The heat source 22 in FIGURE 4 is depicted as a resistive Wire element, but either heat source 21 or 22 may be any conventional heating device for providing the necessary heat. With some materials, the erasure heat above is insufficient to increase conductivity enough to dissipate the electrostatic image. Using the frost member of the present invention, the conductive electrode 15 is readily shorted to the substrate 11 as by a shorting switch 23 to short out the latent image. Uniform illumination should be provided while shorting so that layer 12 does not block charge movement.

FIGURE 5 is an embodiment of a frostable member 17 having a preferred arrangement for conductive strip 16. Thus, in FIGURE 5, conductive strip 16 is formed in two strips, one running the length of each edge frostable member 17. These strips are suitably of an evaporated metal such as aluminum evaporated to a thickness of two microns or more in order for durability. As has been stated previously, evaporated metallic layers that are too thin tend to show discontinuities after use. Two strips 16 are used in this embodiment in order to keep the distance of frostable areas from the point of good electrical contact at a minimum. This is particularly important when the conductivity of layer 15 is fairly low, for example, as when it is about 2 10- mho/cm. For this purpose, it will be understood that in operation both of the strips 16 are connected in common to one side of the potential source while the substrate 11 is connected to the other side of the potential source.

The present concept has been found patricularly useful in arrangements where charging, exposure and development take place simultaneously. When frost development is performed simultaneously with formation of the latent image, the development process tends to increase the conductivity of the photoconductive and thermoplastic layers so that charge from a preliminary charging step is frequently excessively dissipated. The present concept permits continuous application of charge potential without interfering corona wires or other devices between the exposure system and the frostable member during exposure.

While the present invention has been described as carried out in specific embodiments thereof, there is no desire to be limited thereby, but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A deformation imaging member having a conductive electrode deformable in the random ridges and valleys characteristic of frost comprising:

(a) a conductive substrate;

(b) an insulating photoconductive layer in contact with said substrate;

(c) a deformable thermoplastic layer in contact with said photoconductive layer;

((1) an organic layer having a conductivity of at least about 2 x 10- mhos/cm. and being softenable to a viscosity in the range of from about 10 to 10 poises at a temperatur of about to 200 F. coated over said thermoplastic layer; and

(e) a metallic strip applied along at least one edge of said organic layer in such a manner that a deformable image may be formed on the exposed surface of said organic layer.

2. A deformation imaging member according to claim 1 in which said organic layer is polymerized ethylene imine.

3. A deformation imaging member according to claim 1 in which said thermoplastic layer has a thickness of 1 to 6 microns and said organic layer is at least as thin as said thermoplastic layer.

4. A frost photoreceptor comprising:

(a) aconductive layer;

(b) a deformable organic photoconductive layer having a viscosity in the range of about to 10 poises at a temperature between about 90 and 200 F. and a thickness of about 1 to 6 microns coated directly on said conductive layer; and

(c) a deformable organic conductive layer having a conductivity of at least about 2 X 10 mhos/cm. and being softenable to a viscosity in the range of from about 10 to 10 poises at a temperature of about 90 to 200 F. and a thickness of about 1 to 6 microns.

5 A frost photoreceptor according to claim 4 in which said organic conductive layer is polymerized ethylene imine.

6. A method of frost imaging which consists of:

(a) providing a frost photoreceptor comprising a conductive substrate, a deformable organic photoconductive layer having a viscosity in the range of about 10 to 10 poises at a temperature between about 90 and 200 F. and a thickness of about 1 to about 6 microns on said conductive layer, and a deformable organic conductive layer having a conductivity of at least about 2 x 10* mhos/cm. and being soften- :able to a viscosity in the range of about 10 to 10 poises at a temperature of about 90 to about 200 F. and a thickness of about 1 to about 6 microns overlying said organic photoconductive layer;

(b) applying a potential across said photoreceptor while simultaneously selectively illuminating in a manner so as to produce charge variations at the exposed surface of said photoreceptor; and

(c) heating said photoreceptor so as to form a frost image on the exposed surface of said deformable organic conductive layer in the illuminated areas.

7. The process as disclosed in claim 6 wherein said organic conductive layer comprises polymerized ethylene 1m1ne.

8. A method of frost imaging which consists of:

(a) providing a deformation imaging member comprising: a conductive substrate; an insulating photoconductive layer in contact with said substrate; a deformable thermoplastic layer in contact with said photoconductive layer; an organic layer having a conductivity of at least about 2 x 10- mhos/cm. and being softenable to a viscosity in the range of from about 10 to 10 poises at a temperature of about 90 to 200 F. coated over said thermoplastic layer; and a metallic strip applied along at least one edge of said organic layer in such a manner that a deformable image may be for-med on the exposed surface of said organic layer;

(b) applying a potential across said imaging member while simultaneously illuminating in a manner so as to produce charge variations at the exposed surface of said imaging member; and

(c) heating said imaging member so as -to form a frost image on the exposed surface of said organic layer in the illuminated areas.

9. The process as disclosed in claim 8 wherein said organic layer comprises polymerized ethylene imine.

References Cited J. TRAVIS BROWN, Primary Examiner.

JOHN C. COOPER, Assistant Examiner.

US. Cl. X.R. 

